Physical and biogeochemical processes regulating the dynamics of surface CO2 in a large and deep hardwater lake

• Main Author: Perolo, Pascal
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Université de Lausanne, Faculté des géosciences et de l'environnement 2022
• Subjects: permafrost
• Online Access: https://serval.unil.ch/notice/serval:BIB_9DE85404D454; https://serval.unil.ch/resource/serval:BIB_9DE85404D454.P002/REF.pdf; http://nbn-resolving.org/urn/resolver.pl?urn=urn:nbn:ch:serval-BIB_9DE85404D4541

If inland waters have been acknowledged as significant CO2 emitters and reactors of the global carbon cycle, light has been essentially shed on wetlands, permafrost, and humic lakes, under the overwhelming paradigm that lake supersaturation with CO2 arises from metabolic processes. Within this picture, large and deep hardwater lakes such as Lake Geneva have been largely overlooked, considered neutral to the atmosphere. However, those conceptions rely on data that are poorly resolved in both time and space, leading to a deficient understanding of the fine-scale surface CO2 dynamics in large, deep hardwater lakes and major uncertainties on their estimated annual lake-wide CO2 emissions. Using Lake Geneva as a model for large, deep hardwater lake, the main objectives of this doctoral thesis are (i) to reach a high-resolution understanding of the surface CO2 dynamics and fluxes at the lake, (ii) to untie the physical and biogeochemical processes controlling the CO2 fluxes at the lake– atmosphere interface, and (iii) to derive methodological guidelines on the frequency at which the different components of the CO2 fluxes should be monitored to reach representative estimates of annual CO2 fluxes. The CO2 fluxes at the surface of lakes operate through a net diffusive transport, obeying the first Fickian law often expressed as ???? = ????(????w − ????sat), where F is the CO2 gas flux, k is the gas transfer velocity, ????w is the CO2 concentration at the water surface, and ????sat is the CO2 concentration at saturation with the atmosphere. The guideline of this work is the Fickian equation which is decomposed in its individual terms to quantify the role of physical and biogeochemical processes on their dynamics. In that objective, the temporal variation of the lake surface CO2 and gas exchange velocity was measured at an hourly resolution while their spatial component was addressed by comparing the pelagic and littoral environments. This work benefited from the ongoing initiative of off-shore and in-shore stations for high-frequency ...